shithub: femtolisp

ref: 49d1461e441aea2ebb5bd237bad1026723582b85
dir: /3rd/mp/mptov.c/

#include "platform.h"

#define VLDIGITS (int)(sizeof(int64_t)/Dbytes)

/*
 *  this code assumes that a int64_t is an integral number of
 *  mpdigits long.
 */
mpint*
vtomp(int64_t v, mpint *b)
{
	int s;
	uint64_t uv;

	if(b == nil){
		b = mpnew(VLDIGITS*Dbits);
	}else
		mpbits(b, VLDIGITS*Dbits);
	b->sign = (v >> (sizeof(v)*8 - 1)) | 1;
	uv = v * b->sign;
	for(s = 0; s < VLDIGITS; s++){
		b->p[s] = uv;
#ifndef BITS64
		uv >>= Dbits;
#endif
	}
	b->top = s;
	return mpnorm(b);
}

int64_t
mptov(mpint *b)
{
	uint64_t v;
	uint32_t s;

	if(b->top == 0)
		return 0LL;

	if(b->top > VLDIGITS)
		return b->sign > 0 ? INT64_MAX : INT64_MIN;

	v = 0ULL;
	for(s = 0; s < b->top; s++)
		v |= (uint64_t)b->p[s]<<(s*Dbits);

	if(b->sign > 0){
		if(v > INT64_MAX)
			v = INT64_MAX;
	}else{
		v = v > INT64_MAX ? INT64_MIN : -(int64_t)v;
	}

	return (int64_t)v;
}